Reimpregnation resin comprising reaction product of metal complex and furfuryl alcohol

ABSTRACT

Metal complexes are obtained by reacting furfurylamine with a metal carbonyl selected from the group consisting of tungsten carbonyl, molybdenum carbonyl and chromium carbonyl. Multi-cycle reimpregnation resins are obtained by reacting one of these metal complexes with furfuryl alcohol.

BACKGROUND OF THE INVENTION

This invention relates to thermosetting, solventless polymers containingvariable ratios of tungsten, molybdenum or chromium chemically bonded inthe polymer chain which have high char yield and which are particularlyuseful for multi-cycle reimpregnation of a carbon/carbon composite.

With the advent of aerospace products, carbon/carbon composites havinghigh densities have come into widespread use. One or a combination ofthe following three methods for densification of carbon/carboncomposites is commonly employed: (1) high temperature consolidation; (2)chemical vapor deposition; and (3) multi-cycle reimpregnation. Forapplications involving large parts or complex shapes, multi-cyclereimpregnation has been found to be the most effective method forimparting oxidation resistance and energy absorbing characteristicsthrough the use of specifically formulated polymers.

A reimpregnation resin is a thermosetting polymer introduced as a liquidinto the characteristic voids of a carbon/carbon composite. The resin issubsequently cured and heat treated, thus increasing the density of thecomposite. Selected polymers can be used to impart specific desiredcharacteristics to the composite depending upon the ultimateapplication. Viable reimpregnation resins must maintain a suitably lowviscosity during the reimpregnation process and, in addition, exhibit arelatively high char yield. "Multi-cycle reimpregnation" is the termapplied when the reimpregnation process is repeated a number of times.

U.S. Pat. No. 4,185,043 to Robert C. Shaffer discloses thermoplastic andthermosetting polymers which incorporate tungsten and/or molybdenummetal atoms. The metal atoms are incorporated into the polymer byreacting a monomer or polymer containing at least one free carboxylgroup with a reaction product of tungsten or molybdenum carbonyl andpyrrolidine to obtain a polymer. It is disclosed that the polymers areuseful as reimpregnation resins.

SUMMARY OF THE INVENTION

It has now been discovered that the reaction product of furfurylamineand tungsten carbonyl, molybdenum carbonyl or chromium carbonyl reactsdirectly with furfuryl alcohol to produce a suitable multi-cyclereimpregnation polymer. The resulting dark, viscous polymer may beutilized neat or it may be diluted with furfuryl alcohol, a reactivesolvent, or it may diluted with an inert solvent such asdimethylformamide. Because of the relatively low viscosity at moderatetemperatures, the polymers of this inventions may be used in amulti-cycle reimpregnation process without a solvent. By appropriatechoice of the amounts of reactants, precise variation in metal contentmay be achieved while retaining the metal in atomic form in the polymermolecule. The cured resin possesses low porosity and high char yield,characteristics which render it particularly useful for multi-cyclereimpregnation. Very little tungsten is lost during the sequence ofoperations resulting in the final char.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A complex is first prepared by reacting furfurylamine with a metalcarbonyl selected from the group consisting of tungsten carbonyl,molybdenum carbonyl and chromium carbonyl. The reaction of stericallyunhindered amines, although not furfurylamine, with metal carbonyls iswell known in the art, [see G. W. A. Fowles et al, "The Reactions ofGroup VI Metal Carbonyls with Pyrrolidine, Piperazine and Morpholine",Inorganic Chemistry, Vol. 3, No. 2, pages 257-259 (1964); and C. S.Kraihanzel et al., Inorganic Chemistry, Vol. 2, No. 3, pages 533-540(1963)]. Preferably the complexes are prepared by reacting from 4 to 12moles of furfurylamine per mole of metal carbonyl for from 4 to 20 hoursat a temperature of from 60° to 150° C.

The furfuryl alcohol is reacted with the furfurylamine-metal complex bycombining with two materials and heating the reaction mixture preferablywithin the range of about 25° C. to 180° C. for about 5-10 hrs. Theconditions required for completion of the reaction of thefurfurylamine-metal complex with furfuryl alcohol vary, depending on theratios of reactants as set forth in the following table:

    ______________________________________                                        Ratio of Moles                                                                of Complex to                Time                                             Furfuryl alcohol                                                                          Temp. Range      (Approximate)                                    ______________________________________                                        1:3         25° C. to 160° C.,                                                               5.0 hours                                                    then 160° C. to 170° C.                                                          0.5 hour                                         1:5         25° C. to 160° C.,                                                               3.0 hours                                                    then 160° C. to 175° C.                                                          1.5 hours                                        1:7         25° C. to 160° C.,                                                               5.0 hours                                                    then 160° C. to 172° C.                                                          3.0 hours                                        1:9         25° C. to 160° C.,                                                               5.0 hours                                                    then 160° C. to 180° C.                                                          5.0 hours                                        ______________________________________                                    

The amount of metal in the finished resin may be controlled by varyingthe ratio of furfurylamine-metal complex to furfuryl alcohol in thethermoplastic polymer, and by varying the amount of furfuryl alcoholused as the reactive diluent.

The polymers of this invention have the property of being boththermoplastic and thermosetting, i.e., at temperatures of up to about180° C. they are thermoplastic, i.e., they may be heated to obtain a lowviscosity flowable material which, upon cooling, solidifies. At highertemperatures, i.e., above about 200° C., the materials arethermosetting, i.e., curable.

The following example illustrates the best mode contemplated forcarrying out this invention.

EXAMPLE

A mixture of tungsten hexacarbonyl (88 g, 0.25 mole) and furfurylamine(92 ml, 1.00 mole) is heated at about 120° C. with stirring under argonfor about 16 hours. To the cooled red-brown reaction mixture, 100 ml ofa 50% ethanol/50% water solution is added to cause precipitation of thegolden-yellow complex. The solid is isolated by vacuum filtration andwashing with ethanol/water, followed by vacuum drying. The impureproduct is moderately air-sensitive; the pure dry product isconsiderably less so. However, storage excluding air is advisable.Recrystallization, if necessary, is by solution in warm, oxygen-freefurfurlyamine, followed by precipitation with water. The infraredspectrum of the product indicates that it is W(CO)₄ (furfurylamine)₂.The product does not melt, but decomposes gradually above 60° C.

Furfuryl alcohol (2.08 moles) is added to 0.42 mole of the reactionproduct of tungsten hexacarbonyl and furfurylamine. The mixture isgradually heated to 160° C. over five hours with stirring. It is thenmaintained between 160°-170° C. until the desired viscosity is achieved.The resulting dark brown thermoplastic material is viscous-to-solid atroom temperature, depending on the duration of heating. It can bediluted while hot with a reactive polar solvent such as furfuryl alcoholor with an inert polar solvent such as dimethyl formamide. For maximummetal loading, the resulting polymer may be used "neat" as a multi-cyclereimpregnation resin for a carbon/carbon composite by impregnating itinto the voids of the composite. The polymer is then cured by heating at200° C. for 20 hours. This cured thermoset resin, when subsequentlycarbonized at 800° C. for one hour, contains approximately 35% tungstenby weight. The char contains 80-90% of the tungsten present in thepolymer precursor.

What is claimed is:
 1. A polymer comprising the reaction product of (1)furfuryl alcohol and (2) a metal complex comprising the reaction productof furfurylamine and a metal carbonyl selected from the group consistingof tungsten carbonyl, molybdenum carbonyl and chromium carbonyl.
 2. Apolymer as defined in claim 1 wherein said metal carbonyl is tungstencarbonyl.
 3. A polymer as defined in claim 2 wherein said metal carbonylis molybdenum carbonyl.
 4. A polymer as defined in claim 2 wherein saidmetal carbonyl is chromium carbonyl.